1. Field of the Invention
The present invention relates to a product originating from the torrefaction of pieces of wood, to a process for the production of this substance and to a particular application of this product.
2. The Prior Art
It is known that wood which is heated to a temperature of approximately 200.degree. to 300.degree. C. becomes what may be called "torrefied wood", i.e., a product with a high fixed carbon content, a high calorific value, a very low moisture content, (approximately 3%), and which is non-hygroscopic and rot-proof, having retained practically all the pyroligneous compounds.
It has been proposed to bring woody pieces of different origins to the state of torrefied wood in order to agglomerate them using an added binder (FR-A-953,004) or using the tars produced by the wood itself as the binder (CH-A-228,877), to produce a fuel therefrom.
It has also been proposed (EP-A-007,374) to use wood torrefied under a neutral atmosphere without subsequent agglomeration, especially as fuel.
A drawback of torrefied wood, as proposed until now, is that it is produced from waste from forest plantations or from the wood industry, i.e., from materials of very irregular shape and composition. A product which itself is irregular, and which has a variable particle size and especially a wide particle size range results therefrom. Because of this, a product which does not lend itself well to automatic treatment is obtained, due to the fact that it is subject to blockages or vault formations during its movement, and that its permeability, in bulk, is very irregular. These defects may be overcome for example by cutting pieces of wood to uniform size, or by agglomerating fine particles, especially sawdust, but these operations are expensive, and thus reduce the economic advantage of torrefied wood.
The object of the invention is to provide a process for the production of thermal energy from torrefied wood which is more advantageous from the point of view of its regularity and its cost than similar processes currently known.
Another object of the invention is to provide, by way of new products, torrefied wood obtained as intermediate in the above process, the process of its production itself comprising the first stages of this process of thermal energy production. It is clear that the fact of being able to provide the product for other uses is an additional cause for the lowering of energy cost, due to a better use of the investment.